The catalog is intended to list all S stars having known positions of at least roughly the precision of the Henry Draper Catalogue. An S star is a star in whose spectrum the bands of the ZrO molecule are detectable, ordinarily without needing sufficient spectral resolution to resolve the individual rotational lines of a band in its stronger parts. The majority of the stars in the catalog were classified on the basis of the band with a head near 6474 Angstroms, in the red system of ZrO. The catalog contains right ascension and declination (B1900.0), photographic, visual, or infrared magnitudes, spectral types, and designations that give the star's occurrence in various finding lists, including an unpublished one. Nomenclature Note: There are three catalogues of S stars by Stephenson, each being numbered from 1. Care should therefore be taken to make a clear distinction between a) The present catalogue; these objects are designated "GCSS" b) The second edition published in 1984 (catalog <III/168>) these objects are designated "CSS" (Compilation on galactic S stars), also available as Catalogue <III/168> c) A complement to the Second Edition published in 1990 (=1990AJ....100..569S), designated by "CSS2"